Section 12(2)(a) in The Central Goods and Services Tax Act, 2017
(a)the date of issue of invoice by the supplier or the last date on which he is required, under [OMIT] [Omitted 'sub-section (1) of' by Act No. 31 of 2018, dated 29.8.2018.] section 31, to issue the invoice with respect to the supply; or